The invention relates to a control device for a high-pressure injection nozzle for liquid injection media, in which the injection medium is under high pressure at the nozzle and is metered via based on injection time, injection duration and/or injection quantity, in particular, to a control device for a high-pressure fuel injection nozzle for internal combustion engines with self-ignition and a common rail fuel supply.
Injection nozzles of the above-mentioned type are known from EP 0 753 658 A and consist of the nozzle part with the nozzle needle, which is spring-loaded in the closing direction, and a valve piston which is arranged in the axial extension of the nozzle needle. The valve piston is disposed in alignment with the nozzle needle and forms the connection to the actuating device. The nozzle needle is biased toward its closing direction by the high-pressure injection medium so that the nozzle needle is closed between the injections. The pressure space, on the one hand, is delimited by the valve piston, and is connected via a throttle to the high-pressure supply, that is, in common rail injection systems, the common pressurized fuel distribution line. On the other hand, the pressure space is in communication, via a further throttle, to the return of the fuel supply system to a tank. A throttle located in the connection to the return is capable of being shut off via a shut-off member of the actuating device, the shut-off member being formed by a valve ball. The valve ball acting as a shut-off member is operable by a magnet armature, which comprises an armature bolt and an armature plate. The armature plate is longitudinally displaceably on the latter and interacts with the magnet coil of the solenoid valve of the actuating device. The longitudinal displaceability of the armature plate relative to the armature bolt in the opening direction of the shut-off member is limited by a stop for the armature bolt. The armature plate is biased in the direction of this stop by a relatively weak armature spring. In the opposite direction, that is, toward the closing position of the shut-off member, the armature bolt is engaged by a valve spring which, on the one hand, maintains the closing position, but, on the other hand, can be overcome when current is applied to the magnet coil. Then the shut-off member opens and the pressure space is placed in communication with the return by the valve piston by way of the throttle. As a result, the force exerted on the nozzle needle in the closing direction by the valve piston is reduced so that the nozzle needle can be lifted by the high-pressure medium present at the nozzle needle to open the injection orifice.
The magnet armature, consisting of the valve ball forming the shut-off member, the armature bolt and the armature plate, moves back and forth very quickly between the stops in order to carry out the injection operations. The stops are formed on the one hand by the seat surface of the valve ball and, on the other hand, by a housing-side stop for the armature bolt. The corresponding valve opening periods are between 0.2 and 2 ms. The stroke length is approximately 50 .mu.m.
In conjunction with the high pressures to be controlled, the high switching speeds and also the high positive and negative accelerations during impingement on the stops, pronounced elastic oscillations occur. As a result, the valve ball when hitting the stop formed by the sealing seat opens again briefly in spite of the forces acting in the closing direction. In order to prevent such re-opening, the armature plate is mounted movably on the armature bolt, so that the armature plate is pressed by the armature spring against the associated stop on the armature bolt in the opening direction of the valve. When the armature bolt or the valve ball engages the valve seat, the armature plate, as a result of its mass inertia, can move off the stop by overcoming the engagement force exerted thereon by the armature spring. In this way the magnet armature mass forces effective upon engagement are reduced to such an extent that the mass forces of the magnet armature can remain below the pre-stressing force of the valve spring.
In order to accommodate oscillatory effects which occur despite these measures and which influence the injection operations in an uncontrolled way, in particular the respective injection times and injection quantities, the armature includes a region which is filled with the injection medium. In this area, the armature also includes a radial flange which cooperates with a housing-side abutment surface in the opening direction of the shut-off member (valve ball) of the actuating device, so that the opening movement of the armature bolt is damped upon displacement of injection medium located in the gap between the radial flange and abutment surface. This damping however does not eliminate oscillatory effects which emanate from the axially movable armature plate when the shut-off member formed by the valve ball is seated that is to say during the closing of the shut-off member.
When the valve ball impinges onto its seat, the armature plate continues to move in the closing direction of the armature bolt against the force of the armature spring. As a result, the mass forces associated with the deceleration of the armature bolt are reduced in a desirable way. The armature plate moves as far as a respective reversal point against the force of the armature spring and is then forced back by the armature spring into engagement with the stop of the armature bolt. Although the spring force is relatively weak, during impingement onto the stop, mass forces are again generated which, although being much lower, nevertheless can entail a slight movement of the armature bolt in the opening direction of the shut-off member. Even if this does not ultimately lead to an opening but only to a relief of the engagement force with the seat surface, oscillations generated thereby may behave an adverse effect when there is some time overlap in the activation of the solenoid valve, for example, when the main injection follows a pre-injection with a short time delay.
What may be decisive for this is, inter alia, that the mass force occurring during the deceleration of the armature plate is directed counter to the pre-stressing force of the valve spring and thereby reduces the effective pre-stressing force. If the abutment of the armature plate coincides in time with the energization of the magnet, the reduced effective pre-stressing force results in a reduced response time of the solenoid valve. The opposite effect occurs when the magnet is energized prior to abutment.
Further influences may result from the fact that the speed of the magnet armature changes as a whole, specifically from a positive to a negative maximum value when the armature plate engages its stop at the armature bolt. If the magnet is energized during this time, the momentary speed of the magnet armature is effectively the initial speed for the subsequent armature stroke movement. This results in corresponding downward or upward deviations from the opening speed as established from a state of rest. Corresponding influences are also exerted when the magnet is energized during the movement phase of the armature plate that is in intermediate positions of the armature plate.
Since oscillatory actions as they occur, for example, when the armature plate impinges onto the stop, do not suddenly fade away, there may be a so-called armature rebound, a repeated engagement of the armature plate with the stop at decreasing intensity. This results in additional effects which, overall, are detrimental to maintaining the predetermined desired injection values. It is therefore very difficult to meter the injection quantity correctly. In internal combustion engines of vehicles, there maybe an adverse influence both on the deployment of power and on the driving behavior of the vehicle.
Furthermore, U.S. Pat. No. 5,370,355 discloses a quick-switching solenoid valve which is to be used, in particular, in conjunction with fuel injection pumps, for controlling fuel injection. Here, the armature plate and armature bolt form a rigid unit, which is acted upon by a disc spring, which engages on the armature bolt. The bolt is loaded by the spring counter to the lifting direction of the magnet and is supported on the housing side. The disc spring forms a diaphragm, which, at the same time, delimits the magnet space toward the side, which is acted upon by the injection medium. In this region, the armature bolt has a radial flange for engagement with a housing-side abutment surface. When the magnet is de-energized and a corresponding force is generated by the disc spring, the unit formed by the armature plate and armature bolt is damped as a result of the displacement of the injection medium located between the radial flange and abutment surface.
A piston-like slide member forming a 2/2-way valve is provided coaxially to the armature bolt and guided in the housing by which slide member the flow of fuel through the valve is controlled. In its shut-off position, in which fuel flow passage is blocked, the piston-like slide member is in an abutment position relative to the housing under the force of a spring supported on the armature bolt.
The maximum extension and therefore the pre-stress of the spring acting upon the piston-like slide member when current is applied to the magnet and the piston-like slide member is in the opening position is determined by a stop bolt which is co-axial to the armature bolt and is screwed into the latter. It is provided with a stop head, which is engaged by the end face of the piston-like slide member under the force of the spring. When the piston-like slide member is in its closing position corresponding to the position of the armature when the magnet is de-energized, the stop bolt entering the piston-like slide member is lifted off the piston-slide abutment surface formed by the end face and the piston-like slide member is subjected to the load by the spring force, which depends on the lifting clearance. In this arrangement, the piston-like slide member is not damped although the armature, together with the armature bolt, is damped when it drops after the magnet has been de-energized. There is also some uncoupling between the piston-like slide member on the one hand and the armature and armature bolt on the other hand due to the resilient support, but oscillations of the piston-like slide member are not damped when the piston-like slide member engages its seat surface. In any case, this does not address the relevant problems arising from the design of the shut-off member as a piston-like slide member with oscillation-damping slide guides.
It is the object of the present invention to improve the oscillatory behavior of an actuating device of the type mentioned in the introduction thereby to achieve a stabilization of the fuel injection operations.